The present invention relates to a tilt control device for correcting the inclination of an optical disk in the DVD player or the like and a tilt control method.
The DVD player or CD player is provided with an optical pick-up for reading the information recorded on the optical disk by applying a light beam onto the optical disk. If the optical disk is inclined due to plane deflection or warp, the light beam from the optical pick-up is applied obliquely onto the optical disk, and a reflected light is also obliquely directed to the optical pick-up. As a result, the optical pick-up can not receive a part of the reflected light to reproduce a signal correctly. Particularly, the DVD player having a high recording density of disk and a small diameter of light beam is greatly affected by the inclination of disk, so that a correct reproduced signal can not be obtained even with a slight inclination. Thus, to eliminate this nonconformity, it is conventionally commonly practiced that a swingable tilt mechanism is provided to correct the inclination of disk.
FIG. 7 is a schematic diagram showing the tilt control device in the conventional DVD player. 11 denotes an optical disk such as DVD or CD, 12 denotes an optical pick-up for reading the information recorded on the optical disk by applying a light beam onto the optical disk 11, 13 denotes a tilt sensor for optically sensing the inclination of the optical disk 11, 14 denotes a tilt control portion for controlling a tilt motor 15 on the basis of a sensed output of the tilt sensor 13, and 16 denotes a tilt mechanism that is activated by the tilt motor 15. If the optical disk 11 is inclined, the tilt sensor 13 senses the amount of inclination (tilt amount) to send a sensed signal to the tilt control portion 14. The tilt control portion 14 drives the tilt motor 15 on the basis of the sensed signal, so that the tilt mechanism 16 is swung at a predetermined angle by the tilt motor 15. As a result, the optical disk 11 has its attitude corrected in response to swinging of the tilt mechanism 16 to correct the inclination of optical disk so that an illuminating light from the optical pick-up 12 is incident vertically upon the optical disk 11.
However, in the conventional tilt control device, the tilt sensor 13 is provided, apart from the optical pick-up 12, to detect the amount of inclination of the optical disk 11, whereby a separate component of the tilt sensor 13 is needed and there is a drawback that the cost is increased. Further, since the optical pick-up 12 and the tilt sensor 13 are unmatched in position, an error occurs in detecting the amount of inclination, resulting in a problem that the tilt control may not be correctly made.
Thus, noting that without the use of the tilt sensor, the light beam is unfocused on the optical disk if the disk is inclined, a tilt control device for making the tilt control was offered in which an electric current for driving a focus actuator in the optical pick-up is detected, and the amount of inclination of the optical disk is detected based on this electric current (the Unexamined Japanese Patent Application Publication No. 2000-36125). However, in a servo control IC, because a drive current of the focus actuator is not usually monitored, it is difficult to take out this current on the circuit, whereby the IC with a signal terminal of drive current must be developed separately to take out this current. Further, in the tilt control device as disclosed in the above patent, there is a need for a circuit that converts current into voltage, resulting in a complex circuit configuration. Moreover, to make the tilt operation by detecting correctly the amount of inclination of the optical disk, while reproducing the optical disk, it is required to set up a reference position of the tilt prior to reproducing the optical disk. However, no description of this point is made in the above patent.
Another method that uses no tilt sensor is conceived in which a difference signal from a light receiving element of the optical pick-up is employed. For example, a phase difference between two signals obtained from the light receiving element divided into four is detected, a pulse having a time width directly proportional to this phase difference is generated, and the tilt amount is detected on the basis of a sum of pulse widths, as described in the Unexamined Japanese Patent Application Publication No. 2001-266381. However, in this case, a pulse width detecting circuit and an arithmetical operation circuit must be newly added, resulting in a problem that the circuit configuration and the signal processing are more complex.